Electron discharge devices



June 5, 1956 D. c. ROGERS 2,749,476

ELECTRON DISCHARGE DEVICES Filed Jan. 25, 1952 4 Sheets-Sheet l Inventor D. C. R0 (3 E RS June 5, 1956 Filed Jan. 25, 1952 D. C. ROGERS ELECTRON DISCHARGE DEVICES 4 Sheets-Sheet 2 Inventor D C. R0 (3 E RS Jun 1956 D. c. ROGERS V ELECTRON DISCHARGE DEVICES Filed Jan. 25, 1952 4 Sheets-Sheet 5 Inventor DC. R0 6 E R5 June 5, 1956 D. c. ROGERS ELECTRON DISCHARGE DEVICES 4 Sheets-Sheet 4 Filed Jan. 25, 1952 x "FJ I l ll ll 4 iv Inventor DC. R0 (5 E RS United States Patent ELECTRON DISCHARGE DEVICES Douglas Cecil Rogers, London, England, assignor to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application January 25, 1952, Serial No. 268,263

Claims priority, application Great Britain February 2, 1951 2 Claims. (Cl. 315-38) The present invention relates to electron discharge devices for operation as amplifiers or as oscillators in the frequency range 50-450 mc./s.

Below 50 mc./s. lead inductance, stray capacity and electron transit time efiects are not so serious as to preclude the use of carefully designed circuits having lumped circuit elements and thermionic valves Whose electrodes are brought out to pins at the base of the envelope. Beyond the upper end of the above frequency range, circuits using distributed constants, such as transmission lines and cavity resonators, become sufliciently small in size so as not to present undue difficulties in construction, while valves Working on the electron velocity modulation principle (as opposed to charge density modulation) have been developed to overcome the difiiculties associated with electron transit time. Within the quoted frequency band, however, the excessive size of components presents difficulties to the circuit designer and because of lead inductance, difficulties of shielding and the like, the conventional electron charge density modulated valves become very iueflicient. For these reasons it has become common practice to use valves in which at least the control grid is brought out by means of a metal disc sealed between two vitreous portions of the envelope. Such valves are expensive to manufacture compared with the conventional radio type of valve and, as stated above, the cavity or transmission line circuits with which disc-seal valves are associated are bulky and also expensive to manufacture. Particularly when size and weight are of major consideration it is desirable that lumped circuit techniques, using the ordinary low frequency type of valve construction, should be pushed to the limit of efficient use. In unbalanced circuits the grounded grid arrangement is frequently used both for receiving and transmitting circuits, while, in some types of television receivers, use is made in a balanced circuit of a double triode radio valve having a common cathode and separate grids. Using a double triode with common cathode and separate grids it is necessary to provide neutralising arrangements in the circuit whereas the grounded grid circuit has the great advantage that neutralisation is not necessary and the grid and its connection may be used as an efiicient shield between input and output circuits. The grounded grid circuit has also the advantages that the input circuit is not particularly frequency sensitive while the arrangement is inherently a low noise circuit. Although the grounded grid circuit is normally used with disc seal tubes, the present applicant has been able to design unbalanced receiving and transmitting circuits up to frequencies of about 200 mc./ s. using a single valve having leads brought out at the base of the valve envelope and using circuit techniques normally possible' only at lower frequencies.

According to the present invention there is provided an electron dischargedevice comprising in a single envelope having circuit connecting means solely, through base pins and, possibly, top cap connections a pair of triode electrode assemblies each having substantially the same electrical characteristics and adapted for use as a grounded 2,749,476 Patented June 5, 1956 ICC grid amplifier, the control grids of the said assemblies being coupled together internally of the said envelope to operate at the same H. F. potential, the two cathodes being separately connected to respective lead-out pins in the said envelope.

In certain embodiments of the invention the grids may be connected together metallically within the envelope while in others, notably those operating at higher powers, the difiiculty in obtaining identity of characteristics between the two triode sections are such as to make it advisable to cater for separate bias voltages being applied to the grids. In such cases the internal coupling between the grids is obtained by means of a capacitor arranged as part of the valve structure.

Although in a push-pull grounded grid circuit it is, of course, desirable that there shall be no measurable high frequency potential difierence between the grids of the two triode sections, it is not always possible to attain this and I have concluded that, provided the H. F. potential difference between the grids is less than half the corresponding potential dilference between the cathodes of the two triodes, the push-pull circuit is still usable. Accordingly, therefore, in another aspect the invention provides an electron discharge device comprising, within an evacuated envelope provided with circuit connecting means solely through base pins and, possibly, top cap connections: a pair oftriode electrode assemblies of substantially the same electrical characteristics, the grids of the said two triodes being coupled together within the said envelope in such manner that the H. F. potential difference therebetween during operation of the device within the frequency band 50450 mc./ s. in a grounded grid circuit with pushpull input shall be less than half the H. F. potential difference between the cathodes of the said two triodes.

The invention will be described with reference to the accompanying drawings in which:

Figs. 1 and 2 show grounded grid push-pull circuits such as may be used with the discharge devices of the present invention,

Fig. 3 shows an embodiment of the invention such as is used in a receiving circuit, I

Fig. 4 is a diagram of the base of the tube of Fig. 3, reference to which will be made in describing the disposition of the electrode connections,

Fig. 5 shows a transmitting tube embodiment of the invention,

Fig. 6 is a basing diagram of the tube of Fig. 5, and,

Fig. 7 is an exploded view of the component parts of a capacitor included in the construction of the tube shown in Fig. 5.

In the receiving circuit shown in Fig. 1 the electron discharge device 1 comprises a pair or" triode electrode assemblies 2 and 3. The control grids 4 are shown connected together within the envelope and are maintained at ground potential. The cathodes 5 are connected for A. C. purposes through respective capacitors 6 to a dipole aerial 7. For D. C. purposes the cathodes are connected to ground through chokes 8 and bias resistor 9; the resistors 9 are shown shunted by de-coupling capacitors 10. The heaters of the two triode sections are shown connected in parallel to the terminals 11, one of which is at ground potential; a capacitor 12 is shown connected between the two heater supply leads to ensure that these are maintained at the same H. F. potential. The anodes 13 are connected to either side of the tuning condenser 14 of the tuned circuit 15 which comprises a balanced output transformer 16. The D. C. circuit for the anode is completed through the H. T. supply source, the positive terminal of which is connected to a centre tap on the primary of transformer 16. For use in a circuit such as is shown in Fig. 1, the two triode sections should be arranged each to have a working grid-anode mutual conductance of the order of 6.7 .ma./v. in order to match up with a 300 ohm input source impedance.

In the case of tubes designed for transmitting purposes, certain differences of construction and of circuit arrangement are necessary. In the first place the tube will be required to operate under class C conditions which will result in a considerable reduction in gain as compared with the class A conditions of a receiving circuit such as Fig. l. in consequence, in order to obtain a satisfactory power gain, the mutual conductance of the two triode sections must be very much higher than in a receiving tube; thus, for watts output at 400 mc./s. using a 300 v. anode supply, we find that a mutual conductance of about ma./v. for each triode section is desirable.

Secondly, due to class C operation, the input impedance is nonlinear and, in order to preserve an approximately sinusoidal cathode voltage wave form, it is desirable that the cathode circuit be resonant.

Finally, it is normal practice to obtain grid bias for class C amplifiers by grid rectification, using grid blocking capacitors and bias resistors. Therefore, in the transmitting tube case, the grids will not operate at earth D. C. potential and since it is not possible to manufacture valves in which the characteristics of the two halves are absolutely identical, it is desirable that separate D. C. connections can be made to the two triode units; hence it becomes necessary to incorporate an internal coupling capacitor between the grids.

A circuit incorporating the above mentioned modification is shown in Fig. 2 in which like reference numerals identify the same components as in the circuit of Fig. 1. in place of the untuned input circuit of Fig. l a resonant input transformer 17 is shown, the cathodes 5 of the two triode sections being connected to opposite ends of the tuning condenser 18. The heaters for the cathodes are shown connected through choke coils 19 on one side and via their respective cathodes on the other to the heater supply terminals 11. The output circuit is the same as in Fig. l, but in the grid circuit the two grids are coupled together by means of the internal capacitor 20 and each is taken to ground through respective biasing networks 21 and 22.

An embodiment of the invention suitable for use in the circuit of Fig. l is shown in Fig. 3. In this embodiment the glass envelope is provided with a conventional ninepin (Noval) glass base 23, the electrode assembly is mounted between an upper and a lower mica sheet 24 and 25 respectively which are apertured to locate the electrodes and are secured to a pair of support rods 26 and 27 which are welded to respectively adjacent grid pins on opposite sides of the base as indicated by the upper two of the pins marked G in Fig. 4. Separate indirectly heated cathodes 5 have cathode sleeves which are of flat shape connected to the pins identified as C1 and C2 in Fig. 4. The cathode sleeves are coated with electron emissive material on the outer flat surfaces facing anodes 13, which are of channel-shaped sheet metal, the active surfaces of the anodes being the exterior base surfaces of the channels. The anodes are connected to respective base pins A1 and A2. The cathode heaters are connected internally in parallel to the base pins H. Respective pairs of grid support rods 28 and 22 are positioned at either side of the cathodes 5 and carry wire grids 4 surrounding the cathodes. The grids are also connected to the support rods 26 and 27 and to an additional grid pin G next to the anode pin As. We have found that the basing arrangement is quite important and the three grid connections indicated in, Fig. 4 insure low inductance in the leads and also assist in shielding the output circuit from the input. The construction of the grid is such as to insure very effective shielding between cathode and anode circuits and also reduces the direct capacity between the respective anodes to a minimum. The shape of elecrodes 13 is such as to provide large cooling surfaces for the anodes combined with low capacity between them.

4 Due to the low mutual anode capacity and to the fact that the two anode-grid capacities appear in series in the circuit of Fig. l, we have been able to tune the output transformer 16 by means of a conventional trimmer condenser at frequencies as high as 450 mc./s.

In the transmitting tube embodiment shown in Fig. 5 the envelope comprises a B96 glass base 30 and top cap connections 31 for the respective anodes. As in the previous embodiment the electrode structure is mounted between apertured mica discs, identified here by numerals 3;. and 33, which are secured to support rods 34 and 35 connected to pins G1 (Fig. 6) on opposite sides of the base.

Each of the cathodes 36 comprises a rectangular cathode sleeve coated on opposite surfaces with electron emissive material and enclosing a heater. As in the previous embodiment the basing arrangement is important, the cathode sreeves being connected to pins C1 and C2 indicated in Fig. 6 and the respective heaters being taken to pins Hi and H2.

The anode of each triode portion comprises a pair of generally channel-shaped members 37 mounted with the base of the channel opposite and parallel to the respective cathode emitting surface. To assist in heat dissipation each member 37 carries a central fin 38 projecting away from the active anode surface; for convenience of construction the members 37 are in fact each formed of a pair of channel shaped members placed side by side and welded together. The two anode members 37 are con nected together at the upper end of the valve by a bridge member 39. This bridge member is formed so as to provide two vertical channel-shaped end portions 40, which are seated upon the upper mica sheet 32, and a horizontal centre strip portion 41, the portion 41 being continuous with the base or centre of the channel-shaped portion 49. The bridge members 39 assist materially in providing rigidity to the assembly and prevent any movement in the horizontal plane. Each cathode 36 is surrounded by a wire grid 42 wound about a pair of support rods .3. One of the grids is sonnected to the support rods 34 and 35 and thence to the base pins G1. The other grid is connected for D. C. purposes to the Gz. For A. C. purposes the two grids are coupled together by means of a capacitor 42 mounted beneath the lower mica sheet 33. The construction of this capacitor is shown in the exploded view of Fig. 7. It comprises an upper metal shield 43 which is welded to the support rods 34 and 35 and carries a central slot allowing passage for the cathode and grid support rods therethrough; the slot is bounded on either side by upturned walls 44. The grid not connected to the shield 43 is connected to a metal plate 45 sandwiched between a pair of mica sheets 46 which are clamped between the screen 43 and a lower metal sheet 47 by means of the projections 48, 49. These projections are folded over the assembly and bonded to the sheets 47 and 43 respectively.

While the principles of the invention have been described above in connection with specific embodiments, and particular modifications thereof, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the invention.

What I claim is:

1. A grounded-grid type electron discharge device comprising within an evacuated envelope provided with circuit connecting means solely through lead-outs connected to base pins and top caps: a pair of triode electrode assemblies of substantially the same electrical characteristics, means for maintaining the grids of said triodes at the same H. F. potential including a capacitor mounted within said envelope for coupling said two grids, separate connections from the respective cathodes to two lead-outs in said envelope, separate connections from the respective anodes to two other lead-outs in said envelope, 9. pair of sheets of insulating material between which said triode assemblies are mounted, grid and cathode support rods extending through the lower sheet of said pair of sheets, a metallic shield mounted beneath the lower of said pair of sheets of insulating material, said shield comprising a disc having a central slot with up-turned walls on either side of the grid and cathode support rods, the shield being secured to one of the said grid support rods and being thereby in metallic contact with one of the grids, and the said capacitor coupling the two said grids comprising a first metallic sheet clamped with interleaved dielectric sheets between the said shield and a further metal sheet bonded to the shield, the said first metal sheet being in metallic contact with the other one of said grids.

2. A device according to claim 1 in which, said cathodes comprise a pair of substantially flat electron emitting surfaces mounted back-to-back and said anodes comprise a pair of channel shaped members each parallel to a respective one of the said emitting surfaces with the exterior base of the channel opposite thereto, and in which the respective ones of the pair of grids are mounted between the respective cathodes and anodes.

References Cited in the tile of this patent UNITED STATES PATENTS OTHER REFERENCES Brans: Radio Tube Vade-Mecum, 6th Edition, 1946, Editions Techniques P. H. Brans, Antwerp, p. 208 (plate 686), p. 225, p. 200 (plate 479), p. 65. 

